1. Field of the Invention
This invention relates to nonapertured, heavy-weight nonwoven fabric made from hydraulically entangled staple fibers of synthetic organic polymer. More particularly, the invention concerns such a fabric having unusually strong tensile characteristics and high resistance to disentanglement.
2. Description of the Prior Art
Nonwoven fabrics, in which hydraulically entangled staple fibers of synthetic organic polymer form a stable, nonapertured fabric without the presence of resin binder of fiber-to-fiber melt bonds are known in the art. Such fabrics have been manufactured commercially with unit weights that are usually less than 4 oz/yd.sup.2 [136 g/m.sup.2 ]. Bunting et al, U.S. Pat. Nos. 3,493,462, 3,508,308 and 3,560,326 disclose a wide variety of such fabrics with unit weights as high as about 20 oz/yd.sup.2 [680 g/m.sup.2 ]. The commercially manufactured nonapertured fabrics of hydraulically entangled staple fibers are strong and exhibit strip tensile strengths of as high as about 8.5 (lb/in)/(oz/yd.sup.2) [0.44 (N/cm)/(g/m.sup.2)]. However, the heavy-weight fabrics of this type which were disclosed by Bunting et al were relatively weak. For example, such heavy-weight fabrics had strip tensile strengths of 4.39 (lb/in)/(oz/yd.sup.2) [0.226 (N/cm)/(g/m.sup.2)] at a weight of 6.7 oz/yd.sup.2 [227 g/m.sup.2 ] and 1.3 and 1.1 (lb/in)/(oz/yd.sup.2) [0.067 and 0.059 (N/cm)/(g/m.sup.2)] for weights of 10 and 20 oz/yd.sup.2 [339 and 678 g/m.sup.2 ], respectively.
To strengthen these hydraulically entangled staple fiber nonwoven fabrics, various approaches have been made. These included incorporating in the fabrics very long (e.g., 6 inch [15.24 cm]) fibers, fibers of special cross-section, substantially continuous filaments, scrims, layers of continuous filament webs, or specially designed layers. Process modifications intended to provide the increase in strength included treating the staple fiber starting web with hydraulic jets first with the web moving in one direction and then with the web moving in a direction perpendicular to the first direction, adding special chemical agents to the hydraulic jets, utilizing special supports or grills on which the webs were hydraulically treated, and starting with special yarns. Generally, each of these strength increasing modifications were useful for lighter weight fabrics. However, these modifications generally were not satisfactory for preparing strong, heavy weight, nonapertured nonwoven fabrics, which consisted essentially of hydraulically entangled staple fibers of synthetic organic polymer. Such strong, heavy-weight fabrics are desired in uses such as heavy-duty gas filtration. The purpose of this invention is to provide such a strong nonapertured, heavy-weight nonwoven fabric.